The NYPD officer who gunned down an unarmed Bronx teen last year also threatened to shoot the boy’s grandmother, a lawsuit filed yesterday charges.

The family of 18-year-old Ramarley Graham — who was shot in the chest a year ago today by Officer Richard Haste — filed a 108-page lawsuit in Bronx Supreme Court accusing the NYPD of manhandling the teen’s then-58-year-old grandmother and verbally abusing her after the shooting.

“Why did you shoot him? Why you killed him?” cried a heartbroken Patricia Hartley after witnessing her grandson’s shooting.

Haste, a four-year NYPD veteran, pushed the sobbing grandmother into a vase and warned, “Get the f–k away before I have to shoot you, too,” the suit says.

Graham’s family also blamed the NYPD’s “highly aggressive” stop-and-frisk policies for creating an atmosphere that resulted in the killing, legal papers show.

The slain teen’s family also charge that Haste shouldn’t have been a cop in the first place.

“Haste failed his psychological testing exam to become a New York City Police Officer but nevertheless was hired,” the suit alleges.